444 THE BIOLOGY OF MARINE ANIMALS 



there is no evidence that it is involved in synaptic transmission (7, 96, 

 115). 



Echinoderm tissue (muscle, gut) contains appreciable quantities of 

 acetylcholine, and nerve and muscle are rich in cholinesterase. A high 

 sensitivity to acetylcholine has been reported (longitudinal muscle of holo- 

 thurians; retractors of Aristotle's lantern in echinoids), and eserine has an 

 augmentative effect. Following stimulation, a substance having the bio- 

 logical properties of acetylcholine appears in the perfusate. Tunicates are 

 relatively insensitive to acetylcholine and eserine : acetylcholine appears to 

 be absent from tissues, and cholinesterase activity is weak (5, 7, 27, 

 89). 



Conclusions: Cholinergic nerves are recognized in vertebrates, but the 

 evidence for invertebrate phyla is more equivocal. The high sensitivity to 

 acetylcholine, the presence of acetylcholine and cholinesterase and the 

 potentiating effect of eserine point to the existence of cholinergic motor 

 nerves in certain annelids, molluscs and echinoderms. Acetylcholine in 

 these fibres would function as a neuromuscular chemical transmitter. Even 

 within the same phylum, however, the range of sensitivity shows extra- 

 ordinary variation, e.g. in annelids and molluscs. Cholinergic systems in 

 coelenterates and ascidians appear to be precluded by the low sensitivity 

 to acetylcholine shown by these animals. The presence of acetylcholine and 

 high levels of cholinesterase in cephalopod and crustacean nervous systems 

 stands unexplained in the face of low sensitivity to acetylcholine and 

 cholinesterase inhibitors. It appears unlikely that acetylcholine functions 

 as a neuromuscular transmitter in crustaceans (28, 62). 



Effect of Adrenaline. Many invertebrate animals are sensitive to 

 adrenaline. Among those preparations which give a clear-cut positive 

 response to adrenaline are innervated body wall of Aphrodite, Arenicola ; 

 Arenicola-Qxtrovert joined to the oesophagus; holothurian muscle; the 

 retractor of Aristotle's lantern in echinoids; and the proboscis of Balano- 

 glossus. It has a strong stimulatory action on the heart of many inverte- 

 brates (Chapter 3). Adrenaline acts irregularly on the limb muscles of 

 crustaceans, but only in high concentrations (10 -4 ). High levels are also 

 required to affect ascidian body wall. It is without effect on body wall of 

 actiniarians, Branchiomma (polychaete), Pontobdella (leech) and slow 

 adductor muscle of Pecten (7, 76, 93). 



In lower chordates (selachians and teleosts) adrenaline is produced in 

 the suprarenal bodies. Its effect resembles that produced by stimulation 

 of certain visceral nerves (75). 



Chromaffin cells have been identified in nerve cords of leech and several 

 polychaetes, and in the heart of Limulus. The leech ganglion is said to con- 

 tain adrenaline, while the posterior salivary glands of octopods contain 

 noradrenaline. Adrenaline acts as a neuromuscular transmitter and hor- 

 mone in vertebrates, and seemingly in those invertebrates in which 

 adrenaline and chromaffin tissue have been identified. Even in the absence 

 of adrenergic nerves, adrenaline, as a secreted hormone, can affect the 



